Insulated metallic sheathed conductor employing at least one pair of twisted signal carrying wires



Sept. 7, 1965 B. c. DAVIS ETAL 3,205,296

INSULATED METALLIC SHEATHED CONDUCTOR EMPLOYING AT LEAST ONE PAIR OF TWISTED SIGNAL CARRYING WIRES Filed May 22. 1963 STA/NLE'SS STEEL, 0E EQUIVALENT Al. UM/NA MA G/VZ-S/A 0e EQUIVALENT INVENTOR Bayard GDav/s, BY A/w'n Singer 8 Milford I clmpmargJr.

United States Patent INSULATED METALLIC SHEATHED CONDUCTOR EMPLOYING AT LEAST ONE PAIR OF TWISTED SIGNAL CARRYING WIRES Bayard C. Davis, Elmhurst, Alvin Singer, Glenview, and Milford T. Chapman, Jr., Addison, Ill., assignors, by direct and mesne assignments, to Continental Sensing, Inc., Melrose Park, 11]., a corporation of Illinois Filed May 22, 1963, Ser. No. 282,406 2 Claims. (Cl. 17434) This invention relates to shielded conductors and more particularly to an improved shielded conductor constructed so that the pickup of extraneous signals thereby is effectively eliminated.

- It is a prime object of the present invention to provide an improved shielded conductor.

Still another object of the invention is to provide a shielded conductor that is constructed so that the pickup of extraneous signals thereby is effectively eliminated.

A further object of the present invention is to provide an improved shielded conductor that is impervious to moisture and resistant to the adverse effects incident to ambient temperature varitaions.

A more finite object of the present invention is to provide a shielded signal-carrying conductor that is compact and relatively inexpensive in construction, structurally stable, and possesses the desirable quality of flexibility.

Other objects and advantages of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIGURE 1 is an enlarged perspective view of a segment of an improved shielded conductor embodying the features of the present invention; and

FIGURE 2 is a cross-sectional view taken generally along the line 22 in FIGURE 1.

In general, the present invention is directed to an improved shielded conductor which is constructed so as to be impervious to moisture, unaffected by ambient temperature variations and wherein extraneous noise signals are effectively eliminated and not transmitted by the signalcarrying components of the conductor. Preferably, an embodiment of the shielded conductor includes at least a pair of conductive wires that are wrapped or twisted about each other in spaced-apart relation along the entire length of the shielded conductor. A filler of insulating material is densely compacted about the helically-wrapped wires so as to completely surround the wires and fill the regions defined therebetween. A tubular metallic insulating sheath surrounds the compacted filler and is maintained in intimate relation therewith along the entire length of the shielded conductor.

Since the signal-carrying wires are helically wrapped about each other, extraneous signal voltages stemming from inductive eifects are essentially eliminated, and because the helically-wrapped wires are confined within a densely compacted filler that is intimately surrounded by a metallic sheath, the shielded conductor is impervious to moisture and relatively insensitive to ambient temperature variations. Moreover, the metallic sheath precludes extraneous signals, that might otherwise result from capacitive coupling, from being transmitted to the signalcarrying wires.

A shielded conductor embodying the features of the present invention is shown in FIGURES 1 and 2. The illustrated shielded conductor, which is generally designated by the numeral 10, includes a pair of signalcarrying wires 11, a filler 12 that surrounds the wires, and an insulating sheath 13 that encompasses the filler. The wires 11, which can be formed of any of a number of suitable conductive materials, are twisted or helically Patented Sept. 7, 1965 wrapped in generally uniform fashion about each other, and are maintained in spaced-apart relation from each other, along the entire length of the shielded conductor 10 The filler 12 is formed of a suitable temperature-resistant insulating materials (e.g., alumina, magnesia, etc.) that surrounds the wires and is confined within the relatively thin and generally flexible tubular sheath 13 which is preferably formed of a material such as stainless steel. More particularly, the filler 12 is preferably ingranular or similar form and is densely compacted so as to completely surround the helically-wrapped wires and fill the regions defined therebetween. In one embodiment of the invention the filler is compacted so as to assume a generally cylindrical configuration that complements the confining region 14 defined by the tubular sheath 13.

Although the steps of a preferred method of forming the shielded conductor 10 are subject to variation (i.e., depending upon the length of the shielded conductor to be formed, etc), the sheath 13 including the wires 11 confined within and surrounded by the filler 12 is preferably assembled as a relatively compact unit and drawn through a die structure so that the sheath is intimately bonded about the filler. This operation positively compacts the filler about the wires and eliminates void spaces within the shielded conductor.

A shielded conductor 10 as described above can be produced in any desired length and is highly suitable for use in a variety of application. One typical example is the employment of the shielded conductor in a temperature-measuring system requiring one or more thermocouple elements. If, for example, the shielded conductor 10 is employed in a system calling for only a single thermocouple, the wires 11 are formed of suitable dissimilar materials (e.g., Alumel and Chromel) that are terminated to form a thermocouple junction. In such a temperaturemeasuring system, the measuring instrumentalities are preferably positioned remotely from the thermocouple junction formed by the wires 11. Accordingly, the generated thermal E.M.F. produced at the junction must be transmitted or carried by the shielded conductor 10 over a substantial distance.

As is well known, thermal voltages produced at a thermocouple junction by way of the Seebeck effect, are generally not large voltage signals. Accordingly, extraneous noise signals picked up during the transmission of the thermal voltage signals to the measuring devices can totally nullify the accuracy of temperature measurements effected by the system. However, as generally outlined above, the shielded conductor 10 is constructed so that such distorting noise signals do not affect the thermal voltage signals transmitted thereby. That is, the metallic sheath 13 precludes extraneous noise signals from being capacitively coupled to the wires 11. Moreover, since the wires 11 are helically wrapped about each other in generally uniform fashion and are positively maintained in spaced relation to each other by the filler 12, extraneous signals attributable to inductive coupling are effectively eliminated and the possibility of short circuiting therebetween is precluded. Not only is the shielded conductor 10 constructed so that these desirable results are realized without impeding the transmission characteristics of the wires 11, but the shielded conductor is also impervious to moisture, relatively flexible, and is essentially unaffected by ambient temperature variations.

It should be understood that the transmission of a thermal as described above is illustrative of only one of the many applications wherein the shielded condoctor 10 can be employed. In this connection, the shielded conductor 10, if desired, can be constructed with a plurality of signal-carrying wires and can be utilized in various other systems to transmit a distortion-free signal from any suitable signal source to a remote location.

It should be understood that the foregoing is merely illustrative of the invention. Various modifications in the structural and functional features of the shielded conductor can be devised by those skilled in the art without departing from the invention, various features of which are set forth in the accompanying claims.

What is claimed is:

1. A shielded conductor which comprises at least a pair of conductive wires helically wrapped about each other in repeated fashion and in uniform spaced-apart relation along the entire length thereof; a high temperature-resistant insulating material densely compacted in a generally cylindrical configuration so as to completely surround said conductive wires along the length thereof, fill the regions defined therebetween and maintain the conductive wires in said helically-wrapped spaced relation; and an elongated tubular metallic temperature resistant and moisture impervious sheath surrounding said filler in intimate relation with said filler being maintained UNITED STATES PATENTS 2,036,045 3/36 Harris.

2,119,853 6/38 Curtiss 174-34 X 2,341,235 2/44 Palmer 174l18 X 2,856,341 10/58 Kanne 1364 X 3,080,755 3/63 Percy 136-4 X 3,121,038 2/64 Perotte 174-118 X JOHN F. BURNS, Primary Examiner.

JOHN P. WILDMAN, E. JAMES SAX, DARRELL L.

CLAY, Examiners. 

1. A SHIELDED CONDUCTOR WHICH COMPRISES AT LEAST A PAIR OF CONDUCTIVE WIRES HELICALLY WRAPPED ABOUT EACH OTHER IN REPEATED FASHION AND IN UNIFORM SPACED-APART RELATION ALONG THE ENTIRE LENGTH THEREOF; A HIGH TEMPERATURE-RESISTANT INSULATING MATERIAL DENSLEY COMPACTED IN A GENERALLY CYLINDRICAL CONFIGURATION SO AS TO COMPLETELY SURROUND SAID CONDUCTIVE WIRES ALONG THE LENGTH THEREOF, FILL THE REGIONS DEFINED THEREBETWEEN AND MAINTAIN THE CONDUCTIVE WIRES IN SAID HELICALLY-WRAPPED SPACED RELATION; AND AN ELONGATED TUBULAR METALLIC TEMPERATURE RESISTANT AND MOISTURE IMPERVIOUS SHEATH SURROUNDING SAID FILLER IN INTIMATE RELATION WITH SAID FILLER BEING MAINTAINED IN A COMPACT CONFIGURATION SAID WIRES BEING FIXEDLY CONFINED THEREIN IN HELICALLY-WRAPPED SPACED APART RELATION. 